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What pulls the plug on Alaska's Snow Glacier Dammed Lake, draining it every other year?

Laurel Andrews
Snow Glacier Dammed Lake on the Kenai Peninsula on July 17, 2013. The arrow points to a marker at 2,580 feet. Water levels were last measured at 2,590 feet in mid-September, before the dam gave way and water started to drain. Courtesy National Weather Service

Every two years, a pair of glacial lakes fill up, pressure builds, and water releases beneath the glaciers into rivers and lakes in the Kenai Peninsula. Snow Glacier Dammed Lake, which sits roughly 25 miles northeast of Seward, is draining now amid rainy days, prompting flood advisories in the region. 

Like its “Old Faithful” counterpart, Skilak Lake, Snow Glacier Dammed Lake usually releases every other year. Pressure builds as the glacial-dammed lakes fill with water and eventually hydrostatic forces pushes the glacial ice up. The water forces the ice to float and “the whole lake drains out under the glacier” through a well-developed system of tunnels and caves woven underneath the ice, NWS hydrologist Scott Lindsey said in July.

Skilak Lake, east of Soldotna, drained into the Kenai River in September, NWS hydrologist Dave Streubler said. Now, Snow Glacier Lake is draining almost exactly two years after last time, Oct. 25, 2011. When Snow Glacier Lake releases, its waters gush into the Snow River, which connects to Kenai Lake and Kenai River. Water levels rise and can lead to flooding.

The pattern is always the same. Water dumps out “faster and faster,” into Snow River until the lake is completely drained, and then “boom, it just drops right off,” Streubel said.  

Water flows to the mouth of Snow River at rapid speeds. What was 1,400 cubic feet per second before the release – “still quite a bit of water,” Streubel said – is now at 17,500 cubic feet per second, causing water to gush from the mouth of Snow River into Kenai Lake.

Water from Snow Glacier fills the aptly-named Snow Glacier Dammed Lake, which was last measured in mid-September at around 2,590 feet deep. Scientists estimate water levels using painted rocks on the side of the mountain -- Civil air patrols snap photos of the lake and hydrologists estimate its depth. The 2011 release was around 2,610 feet.

For now, bad weather has grounded aircraft, so NWS isn’t sure how much water is left to drain from the lake, and how much of the high water levels is due to heavy rains. More rain in the forecast is “a little bit concerning,” Streubel said. “Best case would be the lake is almost empty.”

A flood advisory is in effect for the Western Kenai Peninsula and Western Prince William Sound, and the Kenai River at Cooper Landing is expected to rise 2 – 3 feet by Tuesday afternoon.

Contact Laurel Andrews at laurel(at)alaskadispatch.com